Triton Occultation - 2017 October 5

Artwork by Liem Bahneman
Prediction   Occultation Star Information   Station Lists   Finder Charts   Observing Tips

Finder Charts for the Occultation Star

Finder Charts with Occultation Star (Off-Center) and Suitable Comparison Stars

5x5 arcminutes:

10x10 arcminutes:

12.5x12.5 arcminutes:

Finder chart with suitable comparison stars, 5x5 arcmin²

Finder chart with suitable comparison stars, 10x10 arcmin²

Finder chart with suitable comparison stars, 12.5x12.5 arcmin²

The arrow in each plot indicates the motion of Triton across the sky; North is up, East is left. The star circled in red is the occultation star; the stars circled in black and labeled with letters are possible comparison stars (see table below).

 

Suitable Comparison Stars

Occultation Star A B C D E F G H I
Distance (arcmin) - 0.9 4.15 4.1 5.3 8.1 8.6 7.1 4.7 4.0
B-V (mag) 0.65 0.65 0.77 0.67 1.10 0.67 0.61 0.62 0.86 0.85
V (mag) 12.66 15.93 13.89 14.17 9.34 13.32 13.11 11.74 13.60 14.39
B (mag) 13.31 16.59 14.66 14.84 10.45 14.00 13.73 12.36 14.46 15.24
g' (mag) 12.92 16.18 14.21 14.42 10.10 13.61 13.37 11.97 13.93 14.75
r' (mag) 12.50 15.71 13.66 14.02 8.98 13.15 12.97 11.60 13.38 14.15
i' (mag) 12.34 15.38 13.49 13.85 8.71 13.02 12.82 11.48 13.16 13.87
Remarks very faint ok faint very bright great great great close companion very faint

All stellar magnitudes are taken from APASS. Preferred comparison stars are highlighted in green.

If you are limited by a small FOV (< 4 arcmin), do not slow down your frame rate, i.e. increase exposure time just to be able to record the only star in direct proximity (star "A"). Instead, if you have a guide scope or an auxiliary imager available, please record the guider images while you are taking science data.
These images allow us to assess sky conditions during the event, even though the guider camera runs at a much slower frame rate than the science camera. In that sense, your guider images can fill in missing information if your FOV is too narrow to record a suitable comparison star during the occultation.
Our priority is to obtain fast image series of the occultation star with good signal. Depending on the dynamic range of your camera, you might be able to record Neptune simultaneously without saturating pixels.
If you manage to keep Neptune below saturation while having a good signal on the occultation star, it is possible to use Neptune for differential photometry, should no other comparison star be in your FOV.

FOV vs Frame Rate: Achieving a faster frame rate is more important than having more comparison stars in the field. If a reduction of sensor area readout speeds up image acquisition, recording one of the preferred comparison stars is sufficient.

Only record full frame if your frame rate is independent of sensor readout area, or you are already recording the occultation star at an optimal speed, i.e. you do not compromise frame rate on the occultation star by keeping a large frame size.

 

Finder Charts with Occultation Star Centered

2x2 arcminutes:

5x5 arcminutes:

Finder chart with suitable occultation star centered, 2x2 arcmin²

Finder chart with suitable occultation star centered, 5x5 arcmin²

10x10 arcminutes:

20x20 arcminutes:

Finder chart with suitable occultation star centered, 10x10 arcmin²

Finder chart with suitable occultation star centered, 20x20 arcmin²